| AIR ALMANAC |
| Navigators in the 1940s had astronomical tables, called Air Almanacs that were essential for navigation. The US issued these every 4 months. They were arranged so as to afford the desired information from a single page for each day. As the day expired, the page was torn out of the book and thrown away. No advanced mathematics was needed to use them, but several table lookups were needed, and some addition. Instead of trying to duplicate or retrieve these tables, we are suggesting that you use the Internet. Go to http://aa.usno.navy.mil/ and select Data Services from the left side panel, scroll down and click on "celestial navigation data" near the bottom of the page. It will bring up this menu as shown below: |
| figure 22 Just fill in the blanks and click on "get data". The Day to be entered is the Day that it is in Greenwich, England at the time of the shot. The local date may be a day ahead of or behind the Greenwich date. When you click on get data, you will see the following: |
| figure 23 The display of the data you get looks like the figure above. You can pick from the blue lines the stars that best fit your direction of flight, and the normal to it. This is a whole lot easier than using the Air Almanac, even if we had one to use. For the selected Object, the columns of interest are Hc for the angle above the local horizon, and Zn, the direction east of true north. The web site has information on what the Altitude Corrections are, and how to apply them. These Corrections are generally much smaller than the intrinsic error in the jittery environment of a fast moving aircraft, and may be ignored. |